1. Cross Reference
U.S. Pat. Nos. 4,673,377, 4,665,775, 4,610,183, and 4,671,140. U.S. patent application Ser. Nos. 665,84 now abandoned and 665,043 now U.S. Pat. No. 4,671,138.
2. Field of the. Invention
The present invention relates to a vehicle power transmission and more particularly to a belt-pulley type steplessly variable transmission. More specifically, the present invention pertains to a belt-pulley type steplessly variable transmission having a novel forward-reverse drive selecting mechanism.
3. Description of Prior Art
It has been proposed to use a belt-pully type transmission for automobile driving systems. In such driving systems it is required to provide the transmission with a selecting mechanism which selectably transmits the engine rotation in either a forward or a reverse direction. Such a selecting mechanism is disclosed, for example, in Japanese Patent Public Disclosure No. 60-164061, wherein two synchronizer mechanisms are used to transmit the engine rotation in a forward and a reverse direction. That is, an input shaft member of the transmission is arranged to engage with a reverse gear through a gear train. An output shaft of the transmission is axially arranged with the input shaft and between the shafts are provided two synchronizer mechanisms, one for engaging the input shaft directly with the output shaft and the other for engaging the output shaft with the reverse gear. In this type of selecting mechanism the reverse gear and the associated gear train are always engaged with the rotating input shaft to be in a driving condition. Therefore, under forward transmission at high speed, friction becomes high between the rotating portions in the reverse gear and the associated gear train, which causes loss in driving force. In addition, provision of two synchronizer mechanisms tends to make the overall system bulky as well as complicated.
Another type of selecting mechanism is disclosed in U.S. Pat. No. 4,529,393, in which a single synchronizer mechanism is provided to transmit the engine rotation in a forward direction. An idle gear is provided to be engaged with a gear on the synchronizer and with a counter gear so as to provide a reverse drive transmission. In this system the synchronizer ring and the idle gear must be shifted in order to select forward and reverse drive transmission, and so the shifting mechanism tends to become complicated.
It has been known that, in an automobile driving system having the above-mentioned type of transmission system, a hydraulic clutch means such as a torque converter and a fluid coupling is provided .between the output member of an engine and the input member of the transmission system. This type of system is preferably provided with a neutral clutch means such as a multiple plate type clutch so that transmission of the engine power can be interrupted to thereby carry out the selecting operation of the transmission system smoothly. Especially, transmission systems without a synchronizer mechanism for a reverse drive transmission such as in U.S. Pat. No. 4,529,393 require the neutral clutch means in order to secure the smooth selecting operation. The provision of the neutral clutch causes to increase the length of the transmission system, which means an increase in the width of the overall engine having such transmission system. This goes against the requirement that the width of the overall engine should be made as narrow as possible in the case it is mounted transversely in an automobile vehicle of the front-drive, front-engine type.